<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="node_modules/jquery/dist/jquery.js"></script>
</head>

<body>
    <ul id="ul">
        <li>hello world</li>
        <li>hello world</li>
        <li>hello world</li>
        <li>hello world</li>
    </ul>
</body>

</html>
<script>
    $("ul").attr("id", "kk"); //给元素添加属性
    // var ul = document.querySelector("#ul").children;
    // var ul = document.querySelectorAll("ul>li");
    // console.log(ul);
</script>